Device for indicating errors in a control line of an electric control units

Abstract

An indicating device for electric control units has a light-emitting diode together with at least two resistors placed between a supply voltage and ground. A control line extends from the control unit and is connected between the two resistors. The control unit controls the potential on the control line in such a manner that when a defect is recognized an indication is provided. An indication is also provided in the event of a short circuit between the control line and the supply voltage, as well as upon an interruption in the control line.

What is claimed is: 
     
       1. An indicating device for an electric control unit having a control line, the indicating device comprising: at least two resistors connected in series and defining a junction point therebetween, the control line being connected to the junction point; and   means, connected in series with the at least two resistors and coupled between a supply voltage and a ground, for indicating a break in the control line upon the occurrence of the break and for indicating a short-circuit between the control line and the supply voltage upon the occurrence of the short-circuit.   
     
     
       2. The indicating device according to claim 1, wherein the means for indicating includes a light-emitting diode connected in a forward direction. 
     
     
       3. The indicating device according to claim 1, wherein the means for indicating includes a lamp. 
     
     
       4. The indicating device according to claim 1, further comprising a zener diode connected between the at least two resistors and the means for indicating, the zener diode being polarized in a reverse direction. 
     
     
       5. The indicating device according to claim 1, wherein the at least two resistors and the means for indicating form an optical display device. 
     
     
       6. The indicating device according to claim 1, wherein the electric control unit includes a transistor for controlling the control line. 
     
     
       7. The indicating device according to claim 6, wherein the transistor controls a potential of the control line so that the potential of the control line is high when the control line is intact and an error condition is detected by the electric control unit. 
     
     
       8. The indicating device according to claim 6, wherein a collector of the transistor is connected to the control line, an emitter of the transistor is connected to the ground, and a base of the transistor is connected to the control unit so that a base potential of the transistor is controlled by the control unit.